The invention relates to agents for deactivating biofilms on surfaces in a variety of aqueous systems, including but not necessarily limited to recreational and industrial water systems, including drilling systems.
Biological fouling is a serious economic problem in both industrial and recreational water systems. Biological fouling is the buildup of a xe2x80x9cbiofilmxe2x80x9d on the surfaces that come into contact with the water in the system. A xe2x80x9cbiofilmxe2x80x9d is the buildup of layers of microorganisms and/or extracellular substances and the dirt and/or debris that becomes trapped in that buildup. Bacteria, fungi, yeasts, diatoms and protozoa are only some of the organisms that cause the buildup of a biofilm.
In recreational waters, biofilms tend to be xe2x80x9cslimeyxe2x80x9d to the touch, and can create a health hazard. In industrial waters, biofouling can interfere with industrial processes, lowering the efficiency of the process, wasting energy, and reducing product quality. In drilling systems, biofouling contributes to the corrosion of expensive drilling equipment.
Biofilm problems are encountered frequently in cooling water systems used in power- generating plants, refineries, chemical plants, and air conditioning systems. Cooling water systems commonly are contaminated with airborne organisms entrained by air/water contact in cooling towers as well as waterbome organisms from the system""s makeup water supply. The water in such systems generally is an excellent growth medium for these organisms. If not controlled, the biofilm that results from such growth can plug towers, block pipelines, and coat heat transfer surfaces with layers of slime, thereby preventing proper operation and reducing the efficiency of the affected equipment.
Biofilms traditionally are controlled using oxidizing agents, which typically are based on chlorine or bromine. Oxidizing systems are effective to control biofilms, but such systems also can corrode valuable metal equipment and may irritate delicate and/or sensitive skin.
Non-oxidizing agents are available to control biofilms, and should avoid the foregoing problems; however, oxidizing biocides tend to be much more effective than non-oxidizing biocides at deactivating a biofilm. Biofilms also tend to require exposure to much higher doses of non-oxidizing agents for much longer periods of time than the dosage and time required to kill microorganisms in a suspension. As a result, non-oxidizing agents tend to be much more expensive to use as biofilm eradicating agents than oxidizing agents.
The current trend is towards using continuous levels of oxidizing biocides to maintain clean water system surfaces and to decrease the risk of contamination by Legionella pneumophila, the bacteria responsible for Legionnaire""s disease. A continuous need exists for non-oxidizing biofilm agents for aqueous systems which are effective to deactivate biofilms at lower doses.
The invention provides an aqueous system comprising a biofilm deactivation agent consisting essentially of one or more alkylamines. In a preferred embodiment, the biofilm deactivation agent also comprises a synergistically effective combination of the alkylamine with specified monomeric quaternary ammonium salts. The biofilm deactivation agent has a xe2x80x9cminimum biofilm deactivation concentrationxe2x80x9d of about 200 or less. The invention also relates to the method of treating an aqueous system with the biofilm deactivation agent.
Very low concentrations of certain alkylamines completely deactivated biofilm bacteria during laboratory testing, both alone and synergistically in combination with certain monomeric quaternary ammonium salts.
The biofilm deactivation agents of the present invention are useful in a wide variety of aqueous systems, including but not necessarily limited to recreational and industrial systems, including aqueous base drilling systems. Industrial systems in which the present invention may be used include, but are not necessarily limited to cooling water systems used in power generating plants, refineries, chemical plants, air conditioning systems, process systems used to manufacture pulp, paper, paperboard, and textiles, particularly water laid nonwoven fabrics.
A wide variety of alkylamines are capable of deactivating biofilm bacteria according to the present invention if they are used at a high enough concentration. Suitable alkylamines are those with a xe2x80x9cminimum biofilm eradication concentrationxe2x80x9d (MBEC) of about 200 or less, preferably about 100 ppm or less, more preferably about 50 ppm or less, and most preferably about 30 ppm or less.
The MBEC is a valuable measurement for determining whether the quantity of given agent that will be required to eradicate a biofilm will be economically and environmentally feasible. The MBEC test was developed by the University of Calgary to evaluate the efficacy of antibiotics and biocides towards biofilms. H. Ceri, et. al., xe2x80x9cThe MBEC Test: A New In Vitro Assay Allowing Rapid Screening for Antibiotic Sensitivity of Biofilmxe2x80x9d, Proceedings of the ASM, 98, p 525 (1998). Ceri, et. al., xe2x80x9cAntifungal and Biocide Susceptibility testing of Candida Biofilms using the MBEC Device,xe2x80x9d Proceedings of the Interscience Conference on Antimicrobial Agents and Chemotherapy, vol. 38, p. 495 (1998); H. Ceri, et. al., xe2x80x9cThe Calgary Biofilm Device: A New Technology for the Rapid Determination of Antibiotic Susceptibility of Bacterial Biofilms,xe2x80x9d Journal of Clinical Microbiology 37 (1999) 1771-1776. The exclusive license for the MBEC technique is believed to be held by MBEC Biofilm Technologies, 665xe2x80x948th Street S.W., Calgary, Alberta T2P 4H5 Canada.
The MBEC technique consists of growing identical 24-hour biofilms on 96 pegs arrayed in 12 rows and 8 columns. The biofilms then are challenged with decreasing concentrations of selected antibiotics and/or biocides. After a certain challenge time (generally one hour), the biofilms are placed in 96 individual wells of growth media and ultra-sonicated to deactivate any surviving organisms. After culturing overnight, the wells are checked for turbidity. Clear, transparent wells indicate complete deactivation of the biofilm. Conversely, turbidity (xe2x80x9cgrowthxe2x80x9d) indicates lack of complete deactivation of the biofilm.
The minimum biofilm deactivation concentration (MBEC) is defined as the minimum concentration of an agent that completely deactivates biofilm bacteria. The MBEC technique provides a potentially powerful and reproducible tool to study the efficacy of biocides and additives towards biofilm deactivation. Unless otherwise indicated, the biofilms used in the examples below consisted of a pure culture of Pseudomonas aeruginosa (ATCC 15442). The reason for this is that Pseudomonas aeruginosa often represents the major biofilm component in industrial and recreational water systems. J. W. Costerton and H. Anwar, xe2x80x9cPseudomonas aeruginosa: The Microbe and Pathogenxe2x80x9d, in xe2x80x9cPseudomonas aeruginosa Infections and Treatmentxe2x80x9d, A. L. Baltch and R. P. Smith (eds), Marcel Dekker, New York, 1994. In addition, Pseudomonas aeruginosa is a gram-negative bacteria. Gram-negative bacteria tend to be more difficult to kill than gram-positive bacteria. In other words, if an agent is effective against Pseudomonas aeruginosa, then persons of ordinary skill in the art would find it reasonable to predict that the agent also would be effective against other microorganisms found in biofilms.
As a general rule of thumb, about 1 pound of a biofilm treatment agent will result in 10 ppm of actives in a 12,000 gallon aqueous system. Alkylamines and blends that are suitable for use in the invention have MBEC""s of about 200 ppm or less, and require about 20 pounds of the alkylamine or blend to effectively treat about 12,000 gallons of water. Preferred alkylamines or blends have the following characteristics: an MBEC of about 100 ppm or less, requiring about 10 pounds/12,000 gallons of water; more preferably an MBEC of about 50 ppm or less, requiring about 5 pounds/12,000 gallons of water; and, an MBEC of about 30 ppm or less requiring about 3 pounds/12,000 gallons of water.
The alkyl group of alkylamines that will produce an MBEC of 200 ppm or less have from about 8 to about 16 carbon atoms, more preferably from about 10 to about 16, even more preferably from about 11 to about 15 carbon atoms, and most preferably from about 12 to about 14 carbon atoms. Preferred alkylamines are primary alkylamines. Dimethylalkylamines also may satisfy the 200 ppm MBEC requirement when the alkyl group has from about 10 to about 16 carbon atoms, preferably from about 12 to about 16 carbon atoms.
MBEC and carbon number are two ways to identify alkylamines that are useful in the present invention. Another way to identify a suitable alkylamine is by its octanol/water coefficient. The octanol/water partition coefficientxe2x80x94Kowxe2x80x94 is defined as the ratio of the solute concentration in the octanol phase to that in the water phase. It is usually expressed as the logarithm of the number. A logKow of 3.0 means that the compound is 1000 times more soluble in octanol than water. High Kow values can be an indicator of bioaccumulation whereby organisms retain a certain amount of a compound in their tissue. Octanol was chosen since it xe2x80x9cmimicsxe2x80x9d the lipids found in organisms and thus forms the basis for a simple assay for potential biological interactions.
The following are calculated octanol/water partition coefficients for selected alkylamines and quaternary amines. Where available, experimentally determined values also are given [from N. Bodor, Z. Gabanyi, and C-K. Wang, Journal of the American Chemical Society, 111, 3783-3786 (1989)]. The calculated values were arrived at using the KowWIN program of the Environmental Science Center of Syracuse Research Corporation (http://esc.syrres.com/esc.htm).
Octanol water coefficients may be measured or calculated using a variety of known methods. The values herein were calculated using the LogKow program developed by the Syracuse Research Center, which may be found on the internet at http://esc.syrres.com/xcx9cesc/logkow.htm. The Log Kow program estimates the log octanol/water partition coefficient (log P) of organic chemicals using the atom/fragment contribution method. Based on the results of these calculations, persons of ordinary skill in the art would expect alkylamines having a calculated partition coefficient of from about 3.5 to about 7.5 to have an MBEC of about 200 ppm or less. Persons of ordinary skill in the art also would expect alkylamines having a calculated partition coefficient of from about 4 to about 6 to have an MBEC that is about 100 ppm or less, preferably 50 ppm or less, and more preferably 30 ppm or less.
Suitable alkylamines are commercially available from Aldrich Chemicals Ltd. or Sigma Chemical Company. Persons of ordinary skill in the art also can make alkylamines using known procedures, such as those described in R. Morrison and R. Boyd. Organic Chemistry (5th Ed. 1987) xc2xa7xc2xa7 26.11-26.13, pp. 945-948, incorporated herein by reference. Dodecylamine also is available from Akzo, Nobel Chemicals Inc. The alkylamines of the present invention are useful alone, or preferably combination with a suitable quaternary ammonium salt. Suitable quaternary ammonium salts are available from a number of sources, including Albemarle Corporation. Suitable combinations of quaternary ammonium salts and alkylamines have an MBEC of about 200 ppm or less, more preferably about 100 ppm or less, even more preferably about 50 ppm or less, and most preferably about 30 ppm or less.
The ratio of alkylamine to the quaternary ammonium salt may be from about 10:1 to about 1:10. Preferably, the ratio is about 1:1. A preferred embodiment is a 1:1 ratio of a primary alkylamine having from about 10 to about 16 carbon atoms to a quaternary ammonium salts comprising substituent groups on the nitrogen atom independently selected from the group consisting of benzyl groups and alkyl groups having from about 8 to about 16 carbon atoms, preferably from about 10 to about 12 carbon atoms, provided that no more than one of said substituent groups comprises a benzyl group. Even more preferably, the primary alkylamine has from about 12 to about 14 carbon atoms and the quaternary ammonium salt is a dialkyldimethyl quaternary ammonium salt wherein the alkyl groups have from about 10 to about 12 carbon atoms. A most preferred embodiment is didecyldimethyl-ammonium chloride with a primary alkylamine having from about 12 to about 14 carbon atoms, most preferably tetradecylamine, most preferably at a 1:1 ratio. Preferably, the quaternary ammonium compound either has a calculated partition coefficient of from about 3.5 to about 7.5, more preferably from about 4 to about 6, or the combination of a selected alkylamine and a selected quaternary ammonium compound has such a calculated partition coefficient.
Although the alkylamine or the combination of alkylamine and quaternary ammonium salt may be used as the sole treatment in a water system to deactivate biofilms, the treatment of the present invention also is useful in systems containing oxidizing agents, including but not necessarily limited to HOBr and HOCl. In a preferred embodiment, the oxidizing agents are used in an amount effective to maintain static control of an aqueous system, and the non- oxidizing agents of the present invention are provided at intervals in order to deactivate any biofilms that may develop in the system.